Lettuce

Encyclopedia of Food and Culture
COPYRIGHT 2003 The Gale Group Inc.

LETTUCE

LETTUCE. Lettuce has been described as a "weedy Cinderella" by T. W. Whitaker (1974) and as the "queen of the salad plants" by Franklin W. Martin and Ruth M. Ruberté (1975). What is this plant that merits two such disparate descriptions? It is certainly the most commonly used salad vegetable, occurring in or under most salads. Many types exist, varying in size, form, leaf shape, color, and taste. All of these types may have evolved from a weedy form that was used in ancient Egypt as a source of cooking oil from pressed seeds, so both descriptions are probably justified.

Among the several lettuce types, most of which are consumed as raw leaves, one is used for its stem instead of its leaves. This lettuce is depicted on the walls of tombs dating back to about 2500 b.c.e., during the Middle Kingdom of ancient Egypt. Lettuce is shown as a long stem with marks indicating where leaves had been removed. At the top of the stem is a tuft of elongated leaves, bluish green in color. This lettuce may have been the one that first was eaten and may have been derived in turn from the type used for seed oil. The blue color is associated with the process in the growth of lettuce called bolting or stem formation. Leaves that form in the development of the head are green. As the process of bolting begins, the leaves become bluish green, signaling the elongation of the stem, which emerges from the interior of the head and eventually produces many small, yellow flowers that mature into small, narrow fruits. The fruits are less than four millimeters long. They look like seeds and usually go by that name.

Oilseed lettuce is a primitive, wild-looking plant that forms no head or rosette of leaves. It bolts early in its growth cycle, forming a thin stem with elongated, narrow leaves. The seeds produced on this stem are about 50 percent larger than those formed on cultivated lettuce. The seeds are pressed to express an oil used in cooking. This is an ancient custom still practiced in twenty-first century Egypt.

Evolution of Lettuce

One can speculate that somewhere in time ancient Egyptians selected, perhaps from oilseed lettuce, plants that bolted more slowly and formed a thick stem that was less bitter than the more primitive type and therefore edible. This new stem lettuce also had somewhat broader leaves. Later, perhaps many centuries later, further selection may have yielded a newer form with a still shorter stem and broader leaves that were appealing enough to eat, the romaine type. From Egypt, romaine lettuce moved around the Mediterranean Sea and to the Middle East. In these areas it was the most commonly grown lettuce in the twenty-first century. The original stem type traveled eastward, eventually reaching China. Numerous mentions of lettuce in ancient literature, beginning with Herodotus in 550 b.c.e., document its travels into Persia, Greece, Rome, and Sicily and later into France, Germany, and England. Use of descriptive names, such as crispa and purpurea, and place names, such as Cappadocian and Cyprian, indicate further proliferation into various distinctive types differing in color, size, leaf shape, and adaptation to specific environments. The various modern butterhead, leaf, and crisphead forms undoubtedly were selected and developed as lettuce spread through Europe. Lettuce reached the shores of the New World with the second voyage of Christopher Columbus in 1494. Many
varieties within the different types were brought to the Western Hemisphere in subsequent years.

The scientific name of lettuce is Lactuca sativa. Lactuca means 'milk forming', sativa means 'common'. It is related to over one hundred wild species of Lactuca and also to sunflower, artichoke, aster, and chrysanthemum. Among the modern types of lettuce are two crisphead forms, iceberg, which forms a large, firm head, and Batavia, which is slightly softer and smaller than iceberg and is popular in Europe. Romaine lettuce has long leaves in a loaf-shaped head. Butterhead lettuce is quite small with oily, soft textured leaves. Red and green leaf lettuces form no head and have leaves with a variety of shapes. Less commonly found are the Latin type, which looks like a small romaine, and the aforementioned stem and oilseed lettuces.

Preparing a Salad

Since lettuce is used mainly in salads, preparation methods are simple, rapid, and informal. The ubiquitous tossed salad is made of lettuce leaves cut up into various-sized pieces. To some people the use of a knife is anathema, and they tear the leaves by hand. The salad maker may use one type of lettuce alone or a mixture of two or more kinds. Depending upon the ingenuity of the salad maker and the availability of edibles, any combination of other vegetables, fruits, and even cheeses or meats can be added to the lettuce. A dressing is added, and the ingredients are mixed together. Salads are vital to many slimming diets, the effectiveness of which can be reinforced or negated by the calorie value of the chosen dressing.

In the United States head lettuce was for many years commonly cut and served as a wedge, covered with mayonnaise or another dressing, and eaten with a knife and fork. This simple salad was served less frequently by the beginning of the twenty-first century. The popular Caesar salad is made only with leaves of romaine lettuce tossed with a special dressing, including a raw egg and small pieces of anchovy. A relative newcomer to the salad scene is mesclun, a mixture of baby leaves consisting of several lettuce types and other leafy vegetables, some of which are fairly exotic. These may include arugula or rocket, actually a partially domesticated weed; a fine-leaved endive called frisée ; mizuna, a small, dark green round leaf from Japan; spinach, beet tops, or chard; red chicory (radicchio); and romaine, butterhead, and red and green leaf lettuces. These leaves are cut in the field by hand, or mowed, when they are no more than ten centimeters long. In parts of the American Southwest wilted lettuce is a favorite salad made by pouring bacon fat over lettuce leaves.

Some salads consist primarily of other vegetables or fruits, such as sliced tomatoes or a scoop of cottage cheese. These are often arranged in a more formal manner than a tossed salad. Lettuce may find its way into these salads as whole or shredded leaves serving as a base for the main constituent.

Lettuce may also be used to make soup, as part of the filling for sandwiches, or as a wrap for holding cooked meat and vegetable mixes. Stem lettuce is consumed raw, like a stalk of celery, in Egypt or as a cooked vegetable in China.

The Biological Human Connection

Lettuce relates to human biology in several ways. The most obvious way is in its role as a food. Some less well-known relationships to human consumption also exist.

As a green vegetable, lettuce contains many of the same nutrients found in other green vegetables, although mostly in lesser amounts. These include vitamins, minerals, water, and fiber but essentially no protein or fat (Table 1). Lettuce is a low to moderate source of vitamins and minerals. Among the various types of lettuce, romaine and leaf varieties exceed crisphead and butter-head varieties for most of the common nutrients. This is directly related to the proportion of dark green leaves in the edible portion. The nutrient contribution of lettuce

source: Adapted from Rubatzky and Yamaguchi (1997) as compiled from several original sources.

compared to other vegetables is affected by the amount consumed. For example, a study by M. A. Stevens in 1974 showed that broccoli has considerably more vitamins and minerals than lettuce but that much more lettuce was consumed than broccoli; therefore the total contribution of nutrients to the diet by lettuce was greater than that of broccoli. This relationship may have changed somewhat as consumption habits changed. Nonetheless lettuce is important for its nutrient content, which complements its usefulness as a diet food because of its high water and fiber content.

Prevention of Cancer

Research in recent years has identified a connection between the consumption of vegetables and certain other foods and beverages and anticarcinogenic activity due to the presence of compounds known as antioxidants. These compounds inhibit the formation of carcinogenic substances in the body. Among the antioxidant compounds in lettuce are 0-beta-carotene, a precursor to Vitamin A, and anthocyanin, which gives the red color in certain lettuce varieties.

The oil pressed from large seeds of certain primitive types of lettuce contributes to a minor food use. The oil is used for cooking and is similar to other oils used for the same purpose. This practice is believed to be hundreds, perhaps thousands of years old.

Nonfood Uses of Lettuce

Turning to nonfood uses, the stems and leaves of lettuce and its wild relatives contain a milky liquid called latex. The latex contains two substances called sesquiterpene lactones, which are the active ingredients in preparations used in some western European countries as a sedative and as a sleep inducer. In folk medicine additional uses for lettuce extracts include treatment for coughs, nervousness, tension, pain, rheumatism, and even insanity. The efficacy of these treatments is not well documented, but some of these effects have been shown in mice and toads.

Another minor nonfood use is drying lettuce leaves for the production of cigarettes without tobacco. Actually leaves of a wild relative of lettuce produce a more tobacco-like appearance. These have been manufactured for use in several brands of cigarettes. Effects on health are not known.

Rarely lettuce may impact human biology in a harmful way. Green leafy vegetables are normally the standard for healthful food, providing vitamins and minerals in a fresh, tasty, and light context. Nitrogen is a vital constituent of chlorophyll, the plant substance that gives the green color and controls photosynthesis. However, green leafy vegetables, including lettuce and spinach, when grown under low light and low temperature conditions in greenhouses in the winter, may accumulate high levels of the nitrate form of nitrogen. In the body nitrate may be converted to compounds that may cause the syndrome called blue baby in infants or may be carcinogenic. Fortunately the likelihood of these consequences is remote, since nitrate accumulation in greenhouse-grown lettuce can be prevented by growing the crop with adequate heat and with supplemental light. Lettuce grown outdoors is not subject to this problem.

Symbolism: Fresh, Cool, Green

The obvious symbolism associated with lettuce is three words, "fresh," "cool," and "green." "Fresh" is a word that many think of as important to health. Lettuce is eaten fresh and raw. In the gardening months many can cut it and eat it almost immediately. It is not that fresh in the store bin of course, but it is still only a few days old. Even the leaves in a packaged salad were growing in the soil shortly before they appeared on the shelf. Lettuce is never frozen or canned.

Lettuce is kept cool. After being cut in the field it is transported to a cooler, where the temperature is quickly reduced to just one degree above freezing. It is transported in refrigerated trucks to a market, where it is kept in a cooler before being placed in a refrigerated bin. Finally, it is purchased by the consumer, taken home, and placed in the refrigerator. This sequence is called the cold chain and is designed to maintain the quality of the lettuce at the time of harvest in the field as long as possible.

Finally, lettuce comes in various shades of green. Even red lettuce contains chlorophyll, which confers the green color, though it may be hidden in the red parts of the leaf. Green means vitamins. Green is a cool color. Many also associate greenness with the health of the planet and with personal health. The process of photosynthesis produces oxygen and sugar converted from carbon dioxide and water. The absorption of carbon dioxide by green plants, from lettuce to trees, helps prevent its accumulation in the air, thus mitigating the greenhouse effect and possible global warming.

The symbolism of these words is so strong that they and similar words, such as "ice," "crisp," "winter," and "spring," have been used repeatedly in various combinations in the names of lettuce varieties. Consider the names Green Ice, Iceberg, Crisp as Ice, Coolguard, Green Towers, Valverde, Valspring, and Winterset.

In ancient Egypt lettuce had sexual symbolism. After completing its vegetative development with the formation of a head or a rosette of leaves, the plant goes into its reproductive phase with the formation of an erect seed stalk bearing flowers. The amount of latex in the plant increases and is under pressure, so if the top of the flowering stalk is cut off, the latex spurts out in a manner reminiscent of ejaculation. The same tomb paintings portraying the ancient stem lettuce also picture the god Min with an erect phallus. Consumption of lettuce may therefore have been thought to increase sexual prowess.

Commercial Production and Marketing

Lettuce has become a major player in commercial production and marketing. Total production worldwide does not compare with the major cereal crops, especially rice, corn, and wheat, or with other commodities, such as sugar crops, beans, and potatoes, but among the vegetables it ranks high. In the United States it is in the top three with tomatoes and potatoes. The key word in contemporary use of lettuce is change: in use of the various types, in development of world markets, in methods of marketing, and in methods of production.

The primary markets for lettuce were, until the late twentieth century, in western Europe and North America, the consequence of its first appearance in the Mediterranean basin followed by movement into northern Europe and then to the New World. In the late twentieth century lettuce became important in Japan, China, Hong Kong, Australia, and some countries of South America and Africa. In the different regions where lettuce was consumed, one type was usually more popular than the others. In northern Europe, for example, the butterhead type predominated. Until the 1970s about 80 percent of the lettuce consumed in England was butterhead, and the other 20 percent was divided among the other major types. In the countries surrounding the Mediterranean nearly all the lettuce was romaine. Stem lettuce was the main type in Egypt and China. In the United States, until the early part of the twentieth century, no one type was strongly dominant. At that time crisphead lettuce began to increase in popularity at the expense of the other types. After the modern iceberg lettuce was developed in the 1940s, 95 percent of the production and consumption was of this type. The first modern iceberg variety was created by T. W. Whitaker of the United States Department of Agriculture and was named Great Lakes, although it was actually bred in California.

Changes in Consumption Patterns

In the late 1970s and early 1980s changes in consumption patterns began. In Britain and Scandinavia iceberg lettuce increased in popularity until it became the dominant type. Iceberg lettuce also made inroads into the butterhead and romaine domains in other western European countries. In the United States, where the iceberg type reigned supreme for most of the twentieth century, romaine, butterhead, and leaf lettuces regained popularity and comprised about one-third of the total production at the end of the twentieth century.

The construction of a home-cooked meal has become a casualty of the modern fast-paced lifestyle. People either eat out more frequently or rely on food packages that are partially processed and therefore can be prepared quickly. Salads are included in this drive for efficiency and speed. Modern supermarkets have dedicated extensive shelf space to packaged salads containing what appears to be an infinite number of combinations of leaves (lettuce, cabbage, radicchio, spinach), cut vegetables (carrots, broccoli, cauliflower), dressings, bacon bits, shredded cheeses, croutons, cut fruits, and more.

Changes have also occurred in production methods. Growing, harvesting, and marketing of lettuce is mainly on a large scale, from planting, with significant inputs of water, chemical fertilizers, and appropriate pesticides, to harvesting, cooling, and shipment to market. Production of food with organic methods has become a rapidly growing industry although it is still a small part of the production picture. Lettuce is included in this cultural change. Most of the change has been in the production of nonheading types, such as romaine and leaf lettuce, but some iceberg lettuce is grown in this way. Organic production emphasizes nonuse of chemical fertilizers and pesticides. This type of production began with small-scale growers, but has been included by growers in large-scale production systems.

Where Lettuce is Grown

The need for coolness is a key factor in the location and magnitude of lettuce production areas. In the early twenty-first century the United States was by far the largest producer of lettuce in the world (Table 2). However, few of the fifty states produce lettuce commercially, and of the ones that do California and Arizona are responsible for over 90 percent of the production in the country. California alone accounts for over 70 percent and actually grows lettuce year-round. In the summer lettuce

Commercial production of lettuce in the United Statesand the European Union

Area in hectares (1 hectare = 2.47 acres), production in millions of metric
tons.

source: Compiled from U.S. Department of Agriculture and
Eurostat statistics for the years shown.

is produced in coastal valleys near the Pacific Ocean, particularly in the Salinas Valley, which is the most important production region in the world. In the winter lettuce is produced in the desert regions of California and Arizona. For short periods in the spring and fall lettuce is grown in the great Central Valley of California. The coolness of the season is the reason for the movement from location to location. Lettuce grows best when the daytime temperature rarely exceeds 70 to 75°F (21 to 24°C). The desert and inland areas are too hot in summer, while the coastal areas are too cold in winter. Those locations and others with similar seasonal climates in other countries, such as eastern portions of England, the Mediterranean Coast, the Negev Desert in Israel, and the southeastern portions of Australia, produce nearly all the commercially grown lettuce in the world.

Lettuce is grown in home gardens worldwide. In warm climates lettuce growing is usually restricted to the spring and fall, when temperatures are more moderate than in summer or winter. Lettuce grows fast and is easy to grow, especially leaf lettuces, which are the ones most commonly found in the backyard garden.

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lettuce

The Columbia Encyclopedia, 6th ed.

Copyright The Columbia University Press

lettuce, annual garden plant (Lactuca sativa and varieties) of the family Asteraceae (aster family), probably native to the East Indies or Asia Minor, possibly as a derivative of the widespread weed called wild lettuce (L. scariola). L. sativa has been grown as a salad plant since antiquity and is unknown in the wild. Three types of lettuce are planted: head, or cabbage, lettuce; the leaf, or loose, type; and Cos lettuce, or romaine. The first forms a tight, crisp, white head; the second has many more leaves and a less compact head, which is white toward its center only. Cos lettuce, or romaine, forms long, upright leaves, which, according to variety, may or may not have to be tied up to blanch and form a head. It is not as commonly planted, but is useful where summers are too hot for the other two varieties. As lettuce has increased in popularity in the United States, forcing it for winter use is becoming an extensive industry, especially near large cities. Much of the winter crop comes from Florida and California. The plant is generally eaten as a salad but may be cooked, as it often is in France. A narcotic from the thickened juice of some Lactuca species has been used as an opium substitute. Among the many north temperate species is L. canadensis, the American wild lettuce. Lettuce is classified in the division Magnoliophyta, class Magnoliopsida, order Asterales, family Asteraceae.

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lettuce

let·tuce
/ ˈletis/
•
n.
1.
a cultivated plant (Lactuca sativa) of the daisy family, with edible leaves that are a usual ingredient of salads. Many varieties of lettuce have been developed with a range of form, texture, and color. ∎
used in names of other plants with edible green leaves, e.g.,
lamb's lettuce,
sea lettuce.
2.inf.
paper money; greenbacks.

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